This invention relates to a road wheel speed sensor for use with an automotive vehicle supported on road wheels and, more particularly, to a vehicle road wheel speed sensor for detecting the speed of rotation of one of the road wheels in response to a pulsating variation in magnetic flux produced with rotation of the one road wheel.
Such a vehicle road wheel speed sensor is disclosed, for example, in Japanese Utility Model Publication No. 3-25275. The conventional vehicle road wheel speed sensor is associated with a rotor mounted for rotation in synchronism with rotation of one of vehicle road wheels to produce a pulse signal having a repetitive rate proportional to the speed of rotation of the one vehicle road wheel. The pulse signal is applied to switch a transistor on and off so as to produce a sensor signal in response to which a control unit calculates the speed of rotation of the one vehicle road wheel. The conventional vehicle road wheel speed sensor is connected to the control unit through three connection lines, that is, power, ground and signal connection lines. With the conventional vehicle road wheel speed sensor, however, it is impossible to detect breakage in the connection lines based upon the sensor signal as will be described in detail.